Optical elements such as a liquid crystal on silicon (LCOS) element are in widespread use. These optical elements are used in a hermetically-sealed state so that properties of the optical elements will not be affected by humidity. Each of the optical elements is hermetically sealed with (i) a housing which houses the optical element and (ii) a lid which closes the housing.
FIG. 6 is an exploded perspective view illustrating a conventionally typical optical device package 100. The optical device package 100 includes (i) an optical element 110, (ii) a housing 120 which houses the optical element 110, and (iii) a lid 130 which closes the housing 120 (see FIG. 6). FIG. 7 is a cross-sectional view illustrating the lid 130 included in the optical device package 100. The lid 130 includes (i) a frame plate 131 having an opening 131a and (ii) a window plate 132 which is a light-transmissive plate (see FIG. 7). The window plate 132 has a lower surface whose outer peripheral part is bonded, via a bonding layer 133, to an opening-surrounding part of an upper surface of the frame plate 131. After light emitted from the optical element 110 passes through the window plate 132, the light goes out of the optical device package 100. When light externally enters the optical device package 100, the light first passes through the window plate 132 and then enters the optical element 110.
Patent Literature 1 discloses a lid obtained by glass frit bonding of (i) a ceramic lid part which corresponds to the frame plate 131 and (ii) a glass window part which corresponds to the window plate 132.